Department of Vegetable Crops, University of California, Davis, California 95616.
Plant Physiol. 1990 Apr;92(4):1029-37. doi: 10.1104/pp.92.4.1029.
Muskmelon (Cucumis melo L.) seeds are germinable 15 to 20 days before fruit maturity and are held at relatively high water content within the fruit, yet little precocious germination is observed. To investigate two possible factors preventing precocious germination, the inhibitory effects of abscisic acid and osmoticum on muskmelon seed germination were determined throughout development. Seeds were harvested at 5-day intervals from 30 to 65 days after anthesis (DAA) and incubated either fresh or after drying on factorial combinations of 0, 1, 3.3, 10, or 33 micromolar abscisic acid (ABA) and 0, -0.2, -0.4, -0.6, or -0.8 megapascals polyethylene glycol 8000 solutions at 30 degrees C. Radicle emergence was scored at 12-hour intervals for 10 days. In the absence of ABA, the water potential (Psi) required to inhibit fresh seed germination by 50% decreased from -0.3 to -0.8 megapascals between 30 and 60 DAA. The Psi inside developing fruits was from 0.4 to 1.4 megapascals lower than that required for germination at all stages of development, indicating that the fruit Psi is sufficiently low to prevent precocious germination. At 0 megapascal, the ABA concentration required to inhibit germination by 50% was approximately 10 micromolar up to 50 DAA and increased to >33 micromolar thereafter. Dehydration improved subsequent germination of immature seeds in ABA or low Psi. There was a linear additive interaction between ABA and Psi such that 10 micromolar ABA or -0.5 megapascal osmotic potential resulted in equivalent, and additive, reductions in germination rate and percentage of mature seeds. Abscisic acid had no effect on embryo solute potential or water content, but increased the apparent minimum turgor required for germination. ABA and osmoticum appear to influence germination rates and percentages by reducing the embryo growth potential (turgor in excess of a minimum threshold turgor) but via different mechanisms. Abscisic acid apparently increases the minimum turgor threshold, while low Psi reduces turgor by reducing seed water content.
香瓜（Cucumis melo L.）种子在果实成熟前 15 至 20 天即可发芽，并且在果实内保持相对较高的含水量，但很少观察到提前发芽。为了研究防止提前发芽的两个可能因素，在整个发育过程中确定了脱落酸和渗透剂对香瓜种子发芽的抑制作用。种子从开花后 30 至 65 天（DAA）每隔 5 天收获一次，并在 0、1、3.3、10 或 33 微摩尔脱落酸（ABA）和 0、-0.2、-0.4、-0.6 或-0.8 兆帕聚乙二醇 8000 溶液的 0、1、3.3、10 或 33 微摩尔的因素组合下新鲜或干燥后进行培养。在 30°C 下以 12 小时为间隔，10 天内记录胚根的出现情况。在没有 ABA 的情况下，从 30 至 60 DAA，抑制新鲜种子发芽 50%所需的水势（Psi）从-0.3 降低至-0.8 兆帕。发育果实内的 Psi 比发育过程中所有阶段发芽所需的 Psi 低 0.4 至 1.4 兆帕，表明果实 Psi 足够低以防止提前发芽。在 0 兆帕下，抑制发芽 50%所需的 ABA 浓度在 50 DAA 之前约为 10 微摩尔，此后增加到>33 微摩尔。脱水可改善不成熟种子在 ABA 或低 Psi 下随后的发芽。ABA 和 Psi 之间存在线性附加相互作用，即 10 微摩尔 ABA 或-0.5 兆帕渗透压导致发芽率和成熟种子百分比相等且具有附加降低效果。ABA 对胚溶质势或含水量没有影响，但增加了发芽所需的表观最小膨压。ABA 和渗透剂似乎通过降低胚生长潜力（超过最小膨压阈值的膨压）来影响发芽率和百分比，但通过不同的机制。ABA 显然增加了最小膨压阈值，而低 Psi 通过降低种子含水量来降低膨压。
